(REUTERS) - The Federal Reserve will purchase bonds on fewer days in May as it continues to reduce the size of its purchase program, to make the purchases more efficient, the Federal Reserve Bank of New York said on Wednesday.

The US central bank said on Wednesday it would cut its monthly bond purchases to US$45 billion (S$56.5 billion) from US$55 billion, comprising US$20 billion in Treasuries purchases and US$25 billion in mortgage-backed debt.

The widely expected reduction came as the Fed looked past a dismal reading on first-quarter US growth and gave a mostly upbeat assessment of the economy's prospects.

As the size of each purchase operation declines the number of buybacks will be reduced to obtain operational efficiency, said the New York Fed, which manages the purchases.

In May the Fed will buy bonds on 16 days, compared with US$30 billion in Treasuries purchases spread over 18 days in April, according to the Fed's schedule, which was released on Wednesday.

The Fed's bond purchases can influence trading patterns during the day as many dealers and investors buy bonds to sell to the Fed before a buyback, sometimes driving up the price.

Prices often fall after the purchases are completed.